The present invention is directed to a method for bonding to the glass core of polymeric clad glass fiber waveguides and in particular, to silicone clad glass fiber waveguides.
Glass optical fibers used for fiber optics applications typically are protected by a covering or cladding, which can be a polymeric material. For example, co-pending and co-assigned U.S. patent application Ser. No. 964,506 filed on Nov. 29, 1978 by Ellis et al, which is incorporated herein by this reference, describes silicone clad glass fiber waveguides.
Methods for terminating such waveguides are required. Bonding to some cladding materials such as silicone claddings is not functional, because the cladding has little strength, and therefore, maintaining the required critical alignment between fiber ends and interconnecting devices is not possible if a bond is made directly to the cladding.
A method for terminating such silicone clad glass fiber waveguides is described in the aforementioned patent application Ser. No. 964,506. The method involves replacing a portion of the low strength silicone cladding with a harder and higher strength termination sleeve. This involves stripping a portion of the silicone cladding from the glass fiber core and then bonding the termination sleeve to the exposed core. The termination sleeve has a sufficiently low refractive index to contain the transmitted light within the fiber core.
It has been noted that when this method is used, the bond formed between the termination sleeve and the glass core can be inadequate. The bond strength can be substantially less than the strength of the glass fiber core itself, and in use, the glass core can accidentally be pulled out of a termination sleeve. Attempts to alleviate this problem by cleaning the outer surface of the glass fiber core with solvent before bonding have been only partially successful.
It is believed that the problem results from a silicone residue being left on the fiber core. The silicone residue that remains on the glass surface even after chemical treatment of the surface is difficult to wet and prevents good adhesion. Even if a bond to the silicone is formed, the bond strength is dependent on the strength of the silicone to glass bond, which is very low. In view of this problem, there is a need for a surface preparation method for bonding a termination sleeve to a polymeric clad glass fiber waveguide.